Hacker Evolution is, ahem, an evolution of Exosyphen's previous hacking games, of which they've developed several over the years. This is a good thing, as the current game is intelligently thought through and polished, and the puzzles cleverly designed (if at times frustratingly hard). That is, of course, a big advantage of reworking the same theme: you improve each time.
Many will compare Hacker Evolution to Introversion's Uplink, also an excellent game in this--well, there aren't enough hacker games to call it a genre, but "of this type" will do. Hacker Evolution =feels= more like you're actually hacking because of a design decision that in almost any other type of game would be obviously incorrect: The game is largely played on the command line.
You're typing in Unix-style commands (paradoxically, this is a PC game with no Linux version). So the keyboard clatters away, and you penetrate the defenses of a remote machine--or get traced by the opposition. In other words, the physical activity is actually what hackers do (albeit this is of course an abstracted simulation), and it feels right. Surprisingly fun, in fact.
In Hacker Evolution, you're a freelance "white hat" hacker dealing with a series of increasingly dire attacks by cyber criminals. It's a level-based game, and each level poses a different puzzle for you to solve--which you do by invading computers, finding data, taking over machines to serve as intermediate nodes to mask your ultimate IP address, and ultimately uncovering the bad guys. The game has some ten levels (which provide enough gameplay to make the price reasonable), but there's also an active modding community at the developer's site, so if you're seriously into the game, you can extend play beyond that.
Nice techno score, too.